package org.g4studio.core.net;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.InetAddress;
import java.util.Date;

/***
 * The TimeUDPClient class is a UDP implementation of a client for the Time
 * protocol described in RFC 868. To use the class, merely open a local datagram
 * socket with {@link org.apache.commons.net.DatagramSocketClient#open open }
 * and call {@link #getTime getTime } or {@link #getTime getDate } to retrieve
 * the time. Then call {@link org.apache.commons.net.DatagramSocketClient#close
 * close } to close the connection properly. Unlike
 * {@link org.apache.commons.net.TimeTCPClient}, successive calls to
 * {@link #getTime getTime } or {@link #getDate getDate } are permitted without
 * re-establishing a connection. That is because UDP is a connectionless
 * protocol and the Time protocol is stateless.
 * <p>
 * <p>
 * 
 * @author Daniel F. Savarese
 * @see TimeTCPClient
 ***/

public final class TimeUDPClient extends DatagramSocketClient {
	/*** The default time port. It is set to 37 according to RFC 868. ***/
	public static final int DEFAULT_PORT = 37;

	/***
	 * The number of seconds between 00:00 1 January 1900 and 00:00 1 January
	 * 1970. This value can be useful for converting time values to other
	 * formats.
	 ***/
	public static final long SECONDS_1900_TO_1970 = 2208988800L;

	private byte[] __dummyData = new byte[1];
	private byte[] __timeData = new byte[4];

	/***
	 * Retrieves the time from the specified server and port and returns it. The
	 * time is the number of seconds since 00:00 (midnight) 1 January 1900 GMT,
	 * as specified by RFC 868. This method reads the raw 32-bit big-endian
	 * unsigned integer from the server, converts it to a Java long, and returns
	 * the value.
	 * <p>
	 * 
	 * @param host
	 *            The address of the server.
	 * @param port
	 *            The port of the service.
	 * @return The time value retrieved from the server.
	 * @exception IOException
	 *                If an error occurs while retrieving the time.
	 ***/
	public long getTime(InetAddress host, int port) throws IOException {
		long time;
		DatagramPacket sendPacket, receivePacket;

		sendPacket = new DatagramPacket(__dummyData, __dummyData.length, host, port);
		receivePacket = new DatagramPacket(__timeData, __timeData.length);

		_socket_.send(sendPacket);
		_socket_.receive(receivePacket);

		time = 0L;
		time |= (((__timeData[0] & 0xff) << 24) & 0xffffffffL);
		time |= (((__timeData[1] & 0xff) << 16) & 0xffffffffL);
		time |= (((__timeData[2] & 0xff) << 8) & 0xffffffffL);
		time |= ((__timeData[3] & 0xff) & 0xffffffffL);

		return time;
	}

	/*** Same as <code> getTime(host, DEFAULT_PORT); </code> ***/
	public long getTime(InetAddress host) throws IOException {
		return getTime(host, DEFAULT_PORT);
	}

	/***
	 * Retrieves the time from the server and returns a Java Date containing the
	 * time converted to the local timezone.
	 * <p>
	 * 
	 * @param host
	 *            The address of the server.
	 * @param port
	 *            The port of the service.
	 * @return A Date value containing the time retrieved from the server
	 *         converted to the local timezone.
	 * @exception IOException
	 *                If an error occurs while fetching the time.
	 ***/
	public Date getDate(InetAddress host, int port) throws IOException {
		return new Date((getTime(host, port) - SECONDS_1900_TO_1970) * 1000L);
	}

	/*** Same as <code> getTime(host, DEFAULT_PORT); </code> ***/
	public Date getDate(InetAddress host) throws IOException {
		return new Date((getTime(host, DEFAULT_PORT) - SECONDS_1900_TO_1970) * 1000L);
	}

}
